Trunk spines of trees: a physical defence against bark removal and climbing by mammals?

Rice physical defenses and their role against insect herbivores

MAIN CONCLUSION

Understanding surface defenses, a relatively unexplored area in rice can provide valuable insight into constitutive and induced defenses against herbivores. Plants have evolved a multi-layered defense system against the wide range of pests that constantly attack them. Physical defenses comprised of trichomes, wax, silica, callose, and lignin, and are considered as the first line of defense against herbivory that can directly affect herbivores by restricting or deterring them. Most studies on physical defenses against insect herbivores have been focused on dicots compared to monocots, although monocots include one of the most important crops, rice, which half of the global population is dependent on as their staple food. In rice, Silica is an important element stimulating plant growth, although Silica has also been found to impart resistance against herbivores. However, other physical defenses in rice including wax, trichomes, callose, and lignin are less explored. A detailed exploration of the morphological structures and functional consequences of physical defense structures in rice can assist in incorporating these resistance traits in plant breeding and genetic improvement programs, and thereby potentially reduce the use of chemicals in the field. This mini review addresses these points with a closer look at current literature and prospects on rice physical defenses.

Blocking then stinging as a case of two-step evolution of defensive cage architectures in herbivore-driven ecosystems

Dense branching and spines are common features of plant species in ecosystems with high mammalian herbivory pressure. While dense branching and spines can inhibit herbivory independently, when combined, they form a powerful defensive cage architecture. However, how cage architecture evolved under mammalian pressure has remained unexplored. Here we show how dense branching and spines emerged during the age of mammalian radiation in the Combretaceae family and diversified in herbivore-driven ecosystems in the tropics. Phylogenetic comparative methods revealed that modern plant architectural strategies defending against large mammals evolved via a stepwise process. First, dense branching emerged under intermediate herbivory pressure, followed by the acquisition of spines that supported higher speciation rates under high herbivory pressure. Our study highlights the adaptive value of dense branching as part of a herbivore defence strategy and identifies large mammal herbivory as a major selective force shaping the whole plant architecture of woody plants.

A new, disjunct species of Bahiana (Euphorbiaceae, Acalyphoideae): Phytogeographic connections between the seasonally dry tropical forests of Peru and Brazil, and a review of spinescence in the family

Bahiana is expanded from 1 to 2 species with the description of B.occidentalis K. Wurdack, sp. nov. as a new endemic of the seasonally dry tropical forests (SDTFs) of Peru. The disjunct distribution of Bahiana with populations of B.occidentalis on opposite sides of the Andes in northwestern Peru (Tumbes, San Martín) and B.pyriformis in eastern Brazil (Bahia) adds to the phytogeographic links among the widely scattered New World SDTFs. Although B.occidentalis remains imperfectly known due to the lack of flowering collections, molecular phylogenetic results from four loci (plastid matK, rbcL, and trnL-F; and nuclear ITS) unite the two species as does gross vegetative morphology, notably their spinose stipules, and androecial structure. Spinescence in Euphorbiaceae was surveyed and found on vegetative organs in 25 genera, which mostly have modified sharp branch tips. Among New World taxa, spines that originate from stipule modifications only occur in Bahiana and Acidocroton, while the intrastipular spines of Philyra are of uncertain homologies.